The effect of hydrostatic pressure upon the hydrogen embrittlement of a HSLA steel

Abstract

Abstract The steels used in sea water needs to be protected against corrosion. The cathodic protection methods is widely used, coupled or not to coating technics. The use of High Strength steels (HSLA) cathodically protected in sea water is faced to the problem of hydrogen embrittlement. This phenomen is controlled by applied protection potential and sea water physico-chemical parameters (temperature, pH, dissolved oxygen contents, etc). The exploitation of ocean is going deeper, so the effect of pressure has to be take in account. Previous works on pressure influence upon hydrogen permeation in steels and theorical approachs concluded on a possible effects of pressure upon the hydrogen embrittlement of high strength steels. Performing tests in a “Corrosion Tank” facility, we studied the behaviour of HSLA steel smooth and Compact Tensile specimens cathodically protected in natural sea water. The results show that an increase of hydrostatic pressure decreases the load threshold of smooth specimens and increases the crack velocity of CT specimens. These results are connected to the influence of pressure on electrochemical phenomenon involved in hydrogen embrittlement: iron and hydrogen reversible potential, hydrogen reaction and calcareous deposits.